The present invention relates to a method and an arrangement for recording on a light-sensitive recording medium, and more particularly to methods and arrangements utilizing an optical element or grating.
It is known to use an optical element or grating for the reproduction of original images on a light-sensitive emulsion or recording medium. Such techniques relate to photolitho and photogravure half-tone processes of reproduction, or in photographic color recording. In these processes continuous tone or tint graduations of the original are replaced by a multiplicity of discrete exposed regions carrying the image of the original.
There are two basic types of lenticular optical elements or gratings: the crossline screen and the contact screen.
In the cross line screen, the surface is generally flat with a pattern of cellular regions superimposed thereon. In the usual embodiment, a sequence of equally spaced parallel lines meet at angles of 90.degree., dividing the surface of the screen into square cellular areas. The screen is usually set at a predetermined distance in front of the light-sensitive emulsion. One particular application of the crossline screen is in multicolor reprographics in which a gradation in color and tint is formed from a discrete number of initial colors.
The disadvantage of the crossline screen is that it is difficult to handle, costly, and results in a low intensity light being transmitted.
The second type of optical element is the contact screen. As the name implies, the screen is in physical contact with the light-sensitive emulsion. One particular application for which the contact screen is therefore not suitable, is in electrophotography.
In multicolor printing or reproduction, it is necessary to change or shift the gratings or screens during the process. In doing so, one is liable to create a Moire pattern in the reproduced image, i.e. an imperfection of wavy lines or geometric shapes in the image caused by a slight offset of two different gratings. Since the pattern will become particularly noticeable after two or more exposures, there is a considerable loss of time and difficulty involved in trying to suppress the pattern during the second or following repetition of the process. Furthermore, the shifting of the gratings requires complicated and expensive machinery.